The spaces between particles are passage ways for microorganisms. Bacteria, flagellates, small ciliates and diatoms meander among the particles, while one algal cell with a strange, horseshoe-shaped chloroplast is standing still. Perhaps this chloroplast is a special type referred to as cyanelle.

Commentary by Prof. Yuji Tsukii, Hosei UniversityThis is a diagonal top view of Paulinella.